1. Field of the Invention
The present invention relates to a fluid passage control device for controlling a fluid pressure actuator such as a tilt cylinder of a power tilt and trim mechanism for an outboard engine.
2. Description of the Prior Art
Some small boats such as motorboats are equipped with a power tilt and trim mechanism having a tilt cylinder for lowering and lifting the outboard engine into and out of the water, and a trim cylinder for changing the angle of the outboard engine underwater.
One such power tilt and trim mechanism comprises first and second on/off valves disposed in fluid passages from a hydraulic pump to respective first and second cylinder chambers in the tilt cylinder, and first and second shuttle valves movably positioned in confronting relationship to the first and second on/off valves, respectively. The first and second shuttle valves have oil passages defined therein and ball valve bodies for selectively opening and closing the oil passages, the oil passages being connected by a communication passage.
When working oil is discharged from the hydraulic pump, the first on/off valve is opened under the pressure of the working oil, opening the fluid passage connected to the first cylinder chamber. The first shuttle valve is also opened under the pressure of the working oil, opening the oil passage thereof. The working oil now flows from the oil passage of the first shuttle valve, pushing open the ball valve body, and flows through the communication passage to the second shuttle valve. Since, however, the ball valve body of the second shuttle valve blocks the working oil, the pressure of the working oil acts on the second shuttle valve. The second shuttle valve is then moved, pushing open the second on/off valve thereby to open the return fluid passage from the second cylinder chamber. The tilt cylinder is now contracted to tilt the outboard engine downwardly.
When the hydraulic pump is shut off, the first on/off valve which has been open so far is closed, and the first shuttle valve returns to close the oil passage thereof with the first on/off valve. The oil passage of the second shuttle valve has been closed by the ball valve body. Consequently, the working oil is trapped in the communication passage which interconnects the shuttle valves. Under the pressure of the working oil trapped in the communication passage, the second shuttle valve is caused to keep the second on/off valve open. The return fluid passage from the tilt cylinder to the hydraulic pump thus remains open. Therefore, when the outboard engine is tilted downwardly, it continuously moved downwardly due to gravity.
U.S. Pat. No. 4,493,659 discloses a tilt-lock mechanism for use with an outboard engine.